1. Field of the Invention
The present invention relates to a photosensitive composition, and more particularly to a photosensitive composition capable of giving a negative type polyimide pattern upon development with an aqueous alkaline solution.
2. Description of Related Art
So far used photosensitive resins are typically polyester acrylate, epoxy acrylate, etc. To obtain a desired pattern upon exposure of these photosensitive resins to light, an organic solvent is used as a developing agent. Such organic solvent developing type, photosensitive resins have such a serious problem as an adverse effect on the environments in addition to safety or sanitary problem during working due to the use of the organic solvent.
In place of the organic solvent developing type, photosensitive resins having such problems, alkali-developable photosensitive resins based on novolak resins, polyvinylphenol, etc. have been proposed and almost all of them have been utilized as positive type thin films having a thickness of a several xcexcm, but these positive type thin films have not always satisfied the heat resistance, preservation stability, pattern embedability, etc. required by FPC (flexible printed substrate) applications.
Furthermore, polyimide resins themselves are insoluble in an organic solvent and therefore have so far relied on such a method of once converting them to organic solvent-soluble polyamic acids, followed by their polyimidization. However, some of polyimide resins themselves are soluble in an organic solvent. For example, polyimide resins disclosed in JP-A-57-131227 and polyamide-imide resins disclosed in JP-A-59-145216 are said to be soluble in an organic solvent and photosensitive. However, the organic solvent for that purpose is aprotic polar solvents including dimethyl-formamide, whereas acetone, benzene, cyclohexanol, etc., on the other hand, are used there for deposition of the resins. That is, the resins are insoluble in these latter organic solvents.
An object of the present invention is to provide a photosensitive composition containing a polyimide as photosensitive component which is by itself soluble in low boiling organic solvents for general purpose use, typically methyl ethyl ketone, and capable of giving a negative type pattern upon development with an aqueous alkali solution.
According to the present invention, there is provided a photosensitive composition, which comprises polyimide, comprising a copolymer of two kinds of diamine compounds consisting of diaminopolysiloxane and a carboxyl group-containing diamine or three kinds of diamine compounds consisting of diaminopolysiloxane, a carboxyl group-containing diamine and an aromatic or alicyclic diamine with a 4,4xe2x80x2-(hexafluoroisopropylidene)-diphthalic acid dianhydride, a photo crosslinking agent and a photo acid-generating agent.
A polyimide comprising a copolymer of two kinds of diamine compounds consisting of diaminopolysiloxane and a carboxyl group-containing diamine or three kinds of diamine compounds consisting of diaminopolysiloxane, a carboxyl group-containing diamine and an aromatic or alicyclic diamine with a 4,4xe2x80x2-(hexafluoroisopropylidene) diphthalic acid dianhydride, can be produced by reacting two kinds of diamine compounds consisting of diaminopolysiloxane and a carboxyl group-containing diamine or three kinds of diamine compounds consisting of diaminopolysiloxane, a carboxyl group-containing diamine and an aromatic or alicyclic diamine with a 4,4xe2x80x2-(hexafluoroisopropylidene)diphthalic acid dianhydride, thereby once forming polyamic acid, and then polyimidizing the polyamic acid. The resulting polyimide can be formed into a photosensitive composition by adding a photo crosslinking agent and a photo acid-generating agent thereto.
For diaminopolysiloxane, one component of two or three kinds of diamine compounds, which react with the carboxylic acid anhydride, compounds represented by the following general formula can be used: 
where R is a divalent hydrocarbon group having 2 to 6 carbon atoms, preferably 3 to 5 carbon atoms; R1 to R4 are each a lower alkyl group having 1 to 5 carbon atoms or a phenyl group; and n is an integer of 0 to 30, preferably 4 to 12.
The compounds include, for example, compounds whose R and R1 to R4 are the following substituents in combination:
Actually, the following commercially available products can be used: Toshiba Silicone products TSL9386, TSL9346 and TSL9306; Toray Dow-Corning product BY16-853U, Shinetsu Chemical product X-22-161AS, Nippon Unicar product F2-053-0 1, etc.
The carboxyl group-containing diamine for use in the present invention includes, for example, 3,5-diaminobenzoic acid, 2,5-diaminoterephthalic acid, 2,2xe2x80x2-bis(aminobenzoic acid), etc. These carboxyl group-containing diamines, when the produced polyimide is to be used as a photosensitive resin, can be used so that the carboxyl group content is about 0.6 to about 3.0% by mole, preferably about 0.7 to about 2.5% by mole in the repetition units [(a) and (b) or (a) to (c) which follow]. Below about 0.6% by mole, the polyimide will be less soluble in an aqueous alkali solution, whereas above about 3.0% by mole it will be too soluble therein.
The aromatic or alicyclic diamine for use in the present invention includes, for example, aromatic diamines such as 3,3xe2x80x2-bis(aminophenyl)-ether, 4,4xe2x80x2-bis(aminophenyl)ether, 1,3-bis(4-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy) phenyl]sulfone, 4,4xe2x80x2- diaminodiphenyosulfone, 3,3xe2x80x2-diminodiphenylsulfone, etc. or alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane, 4,4xe2x80x2-bis(aminocyclohexyl)methane, 3,3xe2x80x2-bis(aminocyclohexyl)methane, etc.
When two kinds of diamine compounds are used, diaminopolysiloxane is used in a proportion of about 20 to about 80% by mole, preferably about 40 to about 70% by mole, whereas carboxyl group-containing diamine is used in a proportion of about 20 to about 80% by mole, preferably about 30 to 60% by mole, where total is 100% by mole. When less than about 20% by mole of diaminopolysiloxane is used, no film can be formed, whereas above about 80% by mole development by an aqueous alkali solution cannot be made anv more. When less than about 20% by mole of carboxyl group-containing diamine is used, light-unexposed regions will be insoluble in the aqueous alkali solution, whereas above about 80% by mole even light-exposed regions are soluble, but the difference in dissolution rate between the light-exposed regions and the light-unexposed regions will be smaller.
When three kinds of diamine compounds are used, diaminopolysiloxane is used in a proportion of about 20 to about 70% by mole, preferably about 30% to about 50% by mole, carboxyl group-containing diamine in a proportion of about 20 to about 70% by mole, preferably about 30 to about 50% by mole, and aromatic or alicyclic diamine in a proportion of about 10 to about 60% by mole, preferably about 20 to about 40% by mole, where total is 100% by mole. When the aromatic or alicyclic diamine is used in such a proportion, the polyimide resulting there from will have a higher light transmission in the ultraviolet zone, for example, a satisfactory photosensitivity even to a film as thick as 50 xcexcm. When the aromatic or alicyclic diamine is used in a proportion of more than about 60% by mole, polyimide will have a reduced solubility in the lower boiling organic solvents for general purpose use.
Reaction between a mixture of diamine compounds and a 4,4xe2x80x2-(hexafluoroisopropylidene)diphthaiic acid dianhydride represented by the following formula: 
is carried out preferably in an aprotic polar solvent such as dimethyl-formamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc., but can be carried out even in a polar solvent such as cresol, pyridine, etc. Actually, the carboxylic acid anhydride is dropwise added to a solution of the mixture of diamino compounds in the polar solvent at about 0xc2x0 to about 10xc2x0 C. and subjected to reaction at about 30xc2x0 C. to 150xc2x0 C., preferably at about 50xc2x0 to about 100xc2x0 C., for about 2 to about 8 hours.
The resulting reaction product is polyamic acid as a polyimide precursor, and thus is subjected to dehydration reaction for polyimidization. Dehydration reaction is carried out, after adjustment of the concentration to about 10 to about 20% by weight with a polar organic solvent, if necessary, at a temperature of about 150xc2x0 to about 250xc2x0 C., preferably about 180xc2x0 to about 200xc2x0 C., for about 2 to about 6 hour, preferably about 2 to about 4 hour, preferably by using a dehydrating agent such as acetic anhydride, pyridine, etc., where it is also effective to use toluene, etc. to subject the formed water to azeotropic distillation.
Siloxanepolyimide, which is a polyimidazation reaction product, can be presumed to be a block copolymer having repetition units (a) and (b) represented by the following general formulae, in case of using two kinds of diamine compounds, consisting of diaminopolysiloxane and 3,5-diaminobenzoic acid as carboxyl group-containing diamine: 
Its weight-average molecular weights Mw (determined by GPC in terms of polystyrene) are about 10,000 to about 50,000, preferably about 15,000 to about 30,000.
Furthermore, in case of using three kinds of diamine compounds consisting of diaminopolysiloxane, 3,5-diaminobenzoic acid and 4,4xe2x80x2-bis(aminophenyl)ether, it can be presumed that a block copolymer having further repetition units (c) represented by the following general formula in addition to the repetition units (a) and (b) represented by the foregoing general formulae: 
Its weight-average molecular weights Mw are about 10,000 to about 100,000, preferably about 20,000 to about 50,000, which is higher than that in case of using the two kinds of diamine compounds.
The thus obtained copolymer is soluble in low boiling organic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, ethyleneglycol monomethyl ether, chloroform, etc. or aprotic polar solvents such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, etc., and thus can be used as an organic solvent solution having a concentration of about 20xe2x80x94about 50 wt. %, preferably about 30xe2x80x94about 45 wt. %. The solution is admixed with a photo crosslinking agent and a photo acid-generating agent, and then dropwise provided onto an alkali-resistant substrate such as a quartz glass substrate, a copper substrate, etc. and subjected to spin coating (about 500xe2x80x94about 2,500 rpm, preferably about 500xe2x80x94about 1,000 rpm, for about 10 seconds) to form a film having a thickness of about 25 to about 50 xcexcm, followed by prebaking at a temperature of about 70xc2x0xe2x80x94about 100xc2x0 C., preferably about 80xc2x0xe2x80x94about 90xc2x0 C. for about 5xe2x80x94about 10 minutes, thereby removing the solvent.
The thus obtained photosensitive polyimide-coated substrate is covered with a desired mask thereon and subjected to ultraviolet ray exposure at a dose of about 150xe2x80x94about 600 mJ/cm2, preferably about 200xe2x80x94about 450 mJ/cm2 and then to postexposure baking at a temperature of about 110xc2x0xe2x80x94about 140xc2x0 C., preferably about 120xc2x0xe2x80x94about 135xc2x0 C. for about 5xe2x80x94about 10 minutes, followed by development with an aqueous solution of an alkaline compound such as potassium hydroxide, sodium carbonate, tetramethyl-ammonium hydroxide, etc., at a temperature of about 30xc2x0xe2x80x94about 50xc2x0 C., thereby giving a clear negative type pattern. The developing solution herein used has a concentration of about 0.5xe2x80x94about 4% by weight, preferably about 0.5xe2x80x94about 3% by weight, and the developing time is preferably within about one minute. After the development, water washing, drying and curing at about 160xc2x0 C. for about 2 hours are carried out.
Preferable photo crosslinking agent for use in the present invention includes, hydroxymethyl group-containing substituted phenols such as 2-hydroxymethyl-4,6-dimethylphenol, 1,3,5-trihydroxymethylbenzene, 3,5-dihydroxymethyl-4-methoxytoluene[2,6-bis(Hydroxymethyl)-p-cresol], etc. The photo crosslinking agent can be used in a proportion of about 1 to about 50 parts by weight, preferably about 3 to about 15 parts by weight, per 100 parts by weight of polyimide. Below about 1 parts by weight, the cross-linking density is so low that no satisfactory polymer matrix is formed and thus the film will be dissolved in the aqueous alkali solution, whereas above 50 parts by weight the solubility of the composition is lowered, so that a crystalline pattern will be formed on the coated surface.
Photo acid-generating agent such as nitrobenzyl-9,10-diethoxy-anthracene-2-sulfonate, diphenyliodonium-9,8-demethoxyanthracene sulfonate, etc. can be used in a proportion of about 1 to about 50 parts by weight, preferably about 3 to about 20 parts by weight, per 100 parts by weight of polyimide. Below about 1 parts by weight, FPC pattern will be partially dissolved in the aqueous alkali solution and will be narrowed, whereas above about 50 parts by weight a crystalline pattern will appear on the coated surface as in the case of the photo crosslinking agent.
The present photosensitive composition formed by adding a photo crosslinking agent and a photo acid-generating agent to a polyimide soluble in low boiling organic solvent for general purpose use is developable in an aqueous alkali solution to form a negative type polyimide pattern with a distinguished patternability. When an aromatic or alicyclic diamine is simultaneously used as a diamine compound, a satisfactory photosensitivity even to a thicker film can be given. Particularly in case of using an alicyclic amine, a satisfactory photosensitivity even to a film as thick as 70 xcexcm can be given.